import pygame
from pygame.sprite import Sprite

class Alien(Sprite):
     """表示單個外星人的類"""
     def __init__(self,ai_settings,screen):
         """初始化外星人并設置其起始位置"""
         super(Alien,self).__init__()
         self.screen = screen
         self.ai_settings = ai_settings

         #加載外星人圖像，并設置其rect屬性
         
         self.image = pygame.image.load('images/alien.bmp')
         self.rect = self.image.get_rect()

         #每個外星人最初都在屏幕左上角附近
         self.rect.x = self.rect.width
         self.rect.y = self.rect.height

         #存儲外星人的準確位置
         self.x = float(self.rect.x)
     def blitme(self):
         """在指定位置繪製外星人"""
         self.screen.blit(self.image,self.rect)
     def check_edges(self):
         """如果外星人位於屏幕邊緣，就返回true"""
         screen_rect = self.screen.get_rect()
         if self.rect.right >= screen_rect.right:
             return True
         elif self.rect.left <=0:
            return True    
     def update(self):
         """向右移動外星人"""
         self.x+=(self.ai_settings.alien_speed_factor*self.ai_settings.fleet_direction)
         self.rect.x = self.x
      
        
